(1) Field of the Invention
The present invention relates to a mobile radio communication system, and more particularly to the mobile radio communication system which adopts the CDMA (Code Division Multiple Access) system.
(2) Description of the Related Art
The CDMA system is more likely to be the representative mobile radio communication system of a radio interface because this system may accommodate lots of user equipments on one band, keep the speech quality excellent and also keep the speech privacy high.
FIG. 23 illustrates an exemplary arrangement of the conventional mobile radio communication system that adopts the CDMA system (referred to as the CDMA system mobile radio communication system).
The mobile radio communication system is arranged to have mobile switching centers (each of which is often referred simply to as the MSC) 801 and 802, radio network controllers (each of which is often referred simply to as the RNC) 803 and 804, node bases 805, 806, 807, 808, 809, 810, a user equipment (which is often referred simply to as the UE) 811. This communication system takes a pyramidal network with the MSCs 801 and 802 located topmost.
The MSCs 801 and 802 are connecting nodes between a radio network and a general switched network. For example, when a subordinate radio network of the MSC 801 issues a call connecting (location registration) request to the outside of the switched network of the MSC 801, the MSC 801 is served to be connected with the corresponding other MSC such as the MSC 802. Further, in a case that a receive request is issued outside the switched network of the MSC 801, if the location information of the destination UE 811 is recognized inside the switched network of the MSC 801, the UE 811 transfers a receive signal to the RNC of the concerned area such as the RNC 803. The connecting node for exchanging packets is also called xGSN (x-GPRS (Global Packet Radio Service) Support Node). In the following description, the MSC 801 or 802 cover this connecting node.
The RNC 803 or 804 performs the radio network control between the MSC 801 and the node bases 805 to 810, the call-connecting (or call-ending) control therebetween, the hand-over control therebetween, and the control of the connecting rate (communication rate) of the UE 811. When originating a call (registering a location), the RNC 803 or 804 notifies the MSC 801 of the switched network of a signal passing through one of the node bases 805 to 810 and then performs the radio networking with the concerned node base, for example, the node base 805. When receiving a call, the RNC 803 or 804 transfers the signal from the MSC 801 to a plurality of node bases located close to the UE 811, for example, the node bases 805, 806 and 807, and then receives a response from the UE 811 through the node base of the area where the UE 811 is located, for example, the node base 805. This operation allows the same connecting control (network control) as that in originating a call to be carried out.
The node bases 805 to 810 form their radio zones (each of which is referred to as a cell) for their respective locations. Further, these node bases have a function of relaying a call control signal (origination and location registration) from the UE 811 to the RNC 803 or 804 and also relaying a radio network control signal from the RNC 803 or 804 to the UE 811.
The CDMA system mobile radio communication system utilizes a cellular system that is arranged to cover a service area with lots of cells. Through this cellular system, the CDMA type mobile radio communication system performs a radio multi-link control and a radio network mobile control for supplying high-quality services.
The radio multi-link control is executed to overlap the cell of one node base with those of the other adjacent node bases so that a plurality of radio networks may be connected with one another and thereby to selectively synthesize or restore the transmission informations from those networks. This selective synthesis and restoration makes it possible to supply high-quality radio communication.
The mobile control is executed to continuously connect and disconnect the radio network (which is referred to as the hand-over operation) with movement of the UE 811 on the assumption of the function of the radio multi-link control. This makes it possible to continue the mobile communication.
The conventional hand-over procedure will be described below.
FIG. 24 illustrates the hand-over operation to be executed with movement of the UE.
In FIG. 24, the UE 811 is moved from a cell 807a of the node base 807 managed by the RNC 803 of FIG. 23 to the cell 808a of the node base 808 managed by the RNC 804. The CDMA system mobile control allows the RNC 803 or 804 to switch the cell 807a to the adjacent cell 808a when the UE 811 is moved. The switching of the cells from one to the other means connection and disconnection of the radio links.
The UE 811 constantly monitors the quality (electric power value) of the adjacent cells based on the information of the hand-over-executable adjacent cells pre-notified by the RNC 803 when a call is connected. For example, in the case of detecting a cell with higher quality than the quality of the cell 807a in communication in the hand-over interval as shown in FIG. 24, the hand-over request for the cell 808a is transmitted to the RNC 803. In a case that the concerned cell 808a is located out of the RNC 803 as shown in FIG. 24, the RNC 803 that has received the hand-over request transmits a request for setting up a radio link to the hand-over destination RNC 804 that manages the cell 808a. If the concerned cell 808a is located inside the RNC 803, the request for setting up a radio link with the destination cell is transmitted to the RNC 803.
If the concerned cell 808a is located outside the RNC 803, the hand-over destination RNC 804 that has received the request for setting up the radio link operates to set up the radio link in association with the node base 808 managed by the RNC 804. At a time, the information of the adjacent cell managed by the hand-over destination RNC 804 is reported to the hand-over source RNC 803.
The hand-over source RNC 803, which has received the report about the information of the adjacent cell of the hand-over destination RNC 804, operates to edit the information of the adjacent cell to be notified to the UE 811 from the existing adjacent cell information of the adjacent hand-over destination cell information and then report the edited cell information to the UE 811.
The adjacent cell information to be used by this hand-over system means the information in which all the adjacent cells around any cell are made active.
The CDMA system mobile radio communication system utilizes a Rake synthesis by which multi-paths delayed from each other are separated in time and synthesized in phase, for the purpose of diffusing the data signal through fast diffusion code series when transmitting the data signal. Further, this communication system keeps the quality of the received signal higher by the effective use of the signal power of the multi-paths. Moreover, this communication system enables to execute the communication through a plurality of cells by overlapping the signals from two or more cells with one another in time when receiving or transmitting the signals.
Another conventional technique has been provided which includes a control station that operates to discriminate the quantity and quality of the speech received from the plurality of node bases and then issues a request for changing the transmission output of the downstream control signal to the node base according to the discriminated result. This control station allows the UE that supports the dual mode to send and receive the upstream and the downstream control signals to and from the node base, which makes it possible to lessen call congestion and prevent the speech quality from being degraded without restricting origination or receive of a call (disconnection of a call). This technique may be referred in the Japanese Unexamined Patent Publication 2000-68928.
The recent introduction of various new techniques leads to improving the transmission speed of the data communication in the mobile station year by year. Moreover, the adoption of the communication system through a plurality of cells also leads to realizing the communication system that may keep the speech hardly disconnected.
However, the ways of use of the radio communication are becoming more and more variable. Moreover, the quality of the radio communication is requested to be higher and higher for some ways of use such as a radio or a TV relay.
For the wired communication, it is common to utilize the dual communication system that secures two lines in communication for securing the quality of communication. However, for the radio communication, no such means is provided, so that it has been difficult to secure the high-quality communication.
Moreover, it has been requested to keep the radio communication the substantially same high quality as that of the wired communication, that is, keep the radio communication hardly disconnected.